This invention relates to an extrusion apparatus having a lip gap adjustment mechanism for controlling sheet thickness.
As illustrated by U.S. Pat. Nos. 2,938,231, 3,940,221 and 4,753,587, an extrusion apparatus having a plurality of temperature-responsive, lip gap adjustment assemblies spaced apart across the width of the apparatus, is known. The lip gap is widened or narrowed as the gap-controlling, bolts or rods expand or contract thermally.
The '231 apparatus utilizes individually controllable, resistance heating wires coiled around and in direct contact with the gap-controlling, adjustment bolts. The '587 apparatus uses individually controllable, cartridge heaters, each of which is situated within a bore having a continuous helical channel for flow of a cooling medium. A cover for the lip adjustment assemblies thereof functions as a guide plate for the outflow of the cooling medium. An insulating member is used.
There is a need for an extrusion apparatus having an improved mechanism for controllably adjusting the lip gap. Advantageously, such an improved apparatus would provide for rapid thermally-controlled, lip gap adjustment.